Furling and reefing are separate, but related activities involving hoisting and lowering sails on yachts and sailboats. Furling is completely retiring a sail from use so that the furled sail no longer presents any cross section to the wind for driving the boat. Reefing, on the other hand, refers to reducing the sail area to provide less cross section to the wind, reducing the driving force of the wind on the sail. Since most furlers are also used as reefers, the terms are used interchangeably herein.
Before the advent of furlers, at least two people were needed to hoist and lower the sails on larger yachts. Prior art furlers are intended to allow a single person to hoist and lower sails on large yachts, even those longer than 40 feet. Many of the first mainsail furlers were mast furlers designed to furl the mainsail within the mast, allowing the lower edge, or foot, of the sail to slide along the boom toward the mast as the sail is furled. Unfortunately, mast furlers increase the weight aloft, affecting the stability of the vessel under sail. Mast furlers are also difficult to maintain, as fixing even simple malfunctions, such as jams, requires someone to go aloft, a dangerous and time-consuming activity.
Boom furlers, on the other hand, are configured to furl the sail inside the yacht's boom, which extends perpendicularly from the mast at the foot of the sail. Depending on the configuration, the foot of the sail may be attached to the mandrel along its length or attached only at the tack and clew (i.e., the forward and aft corners along the foot of the sail). A winding cord attaches the sail to a drum inside the boom. Rotating the drum causes the sail to wind (or unwind) around a mandrel inside the boom. Because the boom furler is close to the deck, boom furlers are easier to maintain than mast furlers and do not affect the stability of the yacht.
Unfortunately, most boom furlers must be installed apart from the mast, creating a space between the mast and the furler where the sail deforms. This deformation tends to increase when the sail is wound down, causing folds in the ends of the winding. In addition, this configuration increases stress on the bolt rope, which is sewn into the sail to aid in feeding the sail into the boom or mast. Increased stress on the bolt rope makes it more difficult to wind or unwind the sail.
Prior art solutions described in U.S. Pat. No. 5,697,314 to Clausin include using pulleys to offset the drum or relieve stress on the bolt rope. Pulleys introduce friction, making it difficult to wind and unwind the sail; they also require linkages that must remain taut. Clausin also discloses a recessed bolt rope slot and bolt rope guide that relieve stress on the bolt rope. U.S. Pat. No. 4,236,475 to Merry teaches a simpler, two-pronged metal guide for aligning the bolt rope with mast, preventing the bolt rope from jamming as the sail is raised or lowered. Neither of these bolt rope guides is sufficiently strong to handle the stresses of larger sails, such as those used on yachts of 40 feet or more in length.